Project Summary/Abstract Chronic visceral pain is the cardinal symptom of patients with irritable bowel syndrome (IBS) affecting up to 15% of the U.S. population. Efficacious and reliable therapeutic intervention is still unavailable despite the tremendous economic burden imposed by visceral pain. Pharmacological treatments of visceral pain in IBS are largely unsatisfactory with side effects outweighing therapeutic benefits. In contrast, neuromodulation (e.g., spinal cord stimulation) as an alternative to drugs has much fewer side effects. Recent advances in neuromodulation of the dorsal root ganglions (DRG) relieves certain somatic and neuropathic pain. Hence, the DRG appears to be a promising target for next-generation neuromodulatory devices to treat IBS-related visceral pain. However, knowledge is missing regarding the topological distribution and molecular profiles of functionally-characterized DRG neurons innervating the colon and rectum (colorectum), especially colorectal nociceptors. This has significantly hindered the further development of DRG neuromodulation that selectively affects a subset of DRG neurons in treating visceral pain in IBS. We aim to leverage our recent technical advances in optical electrophysiology via Ca2+ imaging and single-cell transcriptome assay of sensory neurons to characterize the topology and molecular profiles of colorectal nociceptors in the thoracolumbar and lumbosacral DRG. Three specific aims are proposed. Specific Aim 1 will quantify the topological distribution of mechano- nociceptors of the colorectum in the thoracolumbar and lumbosacral DRG in control and prolonged colorectal hypersensitivity. Specific Aim 2 will quantify the topological distribution of silent nociceptors of the colorectum in the thoracolumbar and lumbosacral DRG in control and prolonged colorectal hypersensitivity. Specific Aim 3 will define the molecular profiles of mechano- and silent nociceptors of the colorectum in the thoracolumbar and lumbosacral DRG in control and prolonged colorectal hypersensitivity. By establishing a high-throughput optical electrophysiology method, we will be able to functionally characterize a large number (>2000) of colorectal DRG neurons (including nociceptors) and reveal their topological distributions in thoracolumbar and lumbosacral DRG. The single-cell transcriptome analysis on colorectal nociceptors will reveal promising targets for chemical neuromodulation of the DRG. The outcomes of this research will guide the design of next-generation neuromodulatory devices that target DRG for effective management of chronic visceral pain while minimizing off-target side effects.